Dual zone climate control front back

I would like to change the dual zone climate control from being the front left and right side to being the front and back of the vehicle. This makes much more sense. In the 2013 Ford Fusion, the only way to heat the back of the vehicle is if you use the vents settings. What doesn't the AUTO setting do it? I would much rather have a vehicle where I can set the temperature for the front passengers to one setting and the back passengers to another.